MARINE ALGA) OF BEAUFORT, N. C. 469 
sporangia and sexual organs on the same or different individuals; antheridia and 
carpogonia on the same or different individuals. 
About 110 species, fresh water and marine, in temperate and tropical regions. 
Genus Acrochetium Negeli. 
Acrochetium, Negeli, 1861, p. 402. 
‘Trentepohlia, Farlow, 1882, p. 108. 
Chantransia, De Toni, 1897, p. 67. 
Thallus filamentous, segmented, monosiphonous, irregularly branched, increasing 
in length by transverse division of the apical cell, branches often terminating in hairs; 
asexual propagation by monospores, occasionally by dispores, tetraspores, or polyspores, 
sporangia occurring singly or in tufts, lateral and sessile on the branches or terminal on 
short ramuli; sexual reproduction by eggs borne in carpogonia, and spermatia; antheridia 
borne in tufts at the apices of short branches; carpogonia borne singly at the apices of 
one to three celled branches; sporocarp naked, bearing a tuft of filaments whose ter- 
minal cells form carpospores; sporangia and sexual organs borne on the same or 
different individuals; moncecious or dicecious; sexual reproduction apparently lacking 
in some species. 
About 60 species, marine and fresh water. 
This genus has had a varied nomenclature. Originally described as Acrochetium, 
it has been called Chantransia by many authors. For a time the group, as now reco- 
nized, was separated into two genera—the species with sexual fruit being placed under 
Chantransia' and those with sexual fruit unknown being referred to Acrochetium. It 
is now generally agreed that this distinction is not valid, but there is still disagreement 
as to the proper name for the genus. As was pointed out by Howe (19144, p. 83), the 
name Chantransia has been used for several other forms and is, moreover, a violation 
of all the codes of nomenclature. The name Acrochetium is therefore to be preferred, 
both because of its priority and because it is less likely to cause confusion. 
Some of the species are distinguished with ease, but others are separated by incon- 
spicuous, apparently intergrading, characters, and are determined with great difficulty. 
It is often impossible to decide with certainty to what species a single given plant 
should be referred. 
KEY TO SPECIES. 
a. Plants growing in hydroids PPE RP ARE IO ie BO8 STOVE OS WTP ILD SOO 2 6. A. infestans (p. wih 
aa? Plants growinrion of inother alps. 1a) eho e ek Se Ek Se SS PRE Ee BODE b. 
b. Upright filaments arising from an external basal disk. . ORR US .7. A. virgatulum neh 473)- 
bb. Upright filaments arising in part from an external or internal basal filament. . Hoctro) dP 
c. Basal filament entirely internal, original basal cell conspicuous, sporangia, antheridia’ 
and carpogonia borne on different plants. . ; a ..5. A. corymbiferum (p. 473). 
cc. Basal filament mostly external, original basal cell i inconspicuous, ‘sporangia, antheridia 
and carpogonia borne on the same plants. . hc : .4. A. affine (p. 471). 
bbb. Upright filaments arising from a single basal ‘cell or r from ¢ a few secondary basal celleng nie 4 d. 
“Plants not visible tomakedeye: Bact tas tis dessd - feaeias ppin sell Se beleg: ld TiAl. reer Oe (p- 470). 
dd. Plants visible to naked eye as a fine velvety fringe or mat. . " tase’. 
e. Basal cell pear shaped, penetrating the host to a depth of 12 2 to : 20 mic... .4. & ‘affine (p. 47). 
ee. Basal cell spherical or nearly so, 12 to 25 mic. in diameter, not conspicuously 
penetrating the host, usually bearing several upright filaments, branches often 
elongated and tapering toward apices. . rs .3. A. hoyttt (p. 470). 
eee. Basal cell spherical, 5 to 8 mic. in diameter, ‘superficial, “usually bearing a single 
gy 28 filament, branches not gn peop not ig gle toward apices 
? 138 SRB AT TRA / , .2. A. dufourii (p. 470). 
